Is there a problem putting tzitiz directly on the body of a child {and not on a undershirt}? Is there any problems wearing the titziz undershirts?
Answer:
There is no formal problem in this.
Having said this, many are particular to wear the tzitzis over an undershirt, so that the garment will not become sweaty and sullied (which is disrespectful for the tzitzis; see also sources). Yet, for young children, there is certainly no need for stringency, and there is generally room for leniency where a degree of discomfort is involved.
See Kaf Hachaim 8:3, who writes, based on kabbalistic principles, that the tzitzis garment should not be worn on the flesh. This is also stated by Rav Chaim Kanievsky (Techeiles Ve’argaman 5), and by Teshuvos Vehanhagos (1:25), for fear that the garment would be considered an “undershirt,” which might be exempt from the obligation of tzitzis. However, the general consensus and custom is that the garment will not become an “undershirt” (just like a shirt worn on the body doesn’t become an undershirt), and that there is no formal problem in wearing tzitzis on one’s body.
